Polyamide curing agents are utilized extensively in many markets for epoxy curing agents including coatings, adhesives, composites, and flooring applications. Polyamide curing agents comprise the reaction products of dimerized fatty acid (dimer acid) and polyethyleneamines, and usually a certain amount of monomeric fatty acid which helps to control molecular weight and viscosity. “Dimerized” or “dimer” or “polymerized” fatty acid refers, in a general way, to polymerized acids obtained from unsaturated fatty acids. They are described more fully in T. E. Breuer, ‘Dimer Acids’, in J. I. Kroschwitz (ed.), Kirk-Othmer Encyclopedia of Chemical Technology, 4th Ed., Wiley, New York, 1993, Vol. 8, pp. 223-237.
Dimer acid is usually prepared by the acid catalyzed oligomerization under pressure of certain monomeric unsaturated fatty acids, usually tall oil fatty acid (TOFA), though sometimes other vegetable acids such as soya fatty acid or cottonseed fatty acid are used. Commercial products generally consist of mostly (>70%) dimeric species, with the rest consisting mostly of trimers and higher oligomers, along with small amounts (generally less than 5%) of monomeric fatty acids. Common monofunctional unsaturated C16 to C22 fatty acids also employed with the dimer acids in making polyamides include tall oil fatty acid (TOFA), soya fatty acid, cottonseed fatty acid or the like.
Any of the higher polyethylene polyamines can be employed in the preparation of polyamide curing agents, such as diethylenetriamine (DETA), triethylenetetramine (TETA), tetraethylenepentamine (TEPA), pentaethylenehexamine (PEHA), hexaethyleneheptamine (HEHA), and the like, though in actual commercial practice the polyethylene polyamine most commonly employed is TETA.
In addition, other monofunctional or difunctional carboxylic acids, or other multifunctional amines may be incorporated into the condensation process in order to provide specialized property enhancements.
Polyethylene polyamines are currently manufactured from the reaction of ammonia with either ethylene dichloride or ethanolamine. As new manufacturing assets are built to produce polyethylene polyamines, there is a tendency to favor the ethanolamine process, as it is less corrosive to the manufacturing equipment, and hence more economical. Unfortunately, the ethanolamine process generally produces less TETA than the ethylene dichloride process, and therefore prices for TETA are increasing relative to the prices for other polyethylene polyamines. There is therefore a need for more economical alternatives to TETA in the manufacture of polyamide curing agents. However, it would be advantageous if such an amine would have a molecular weight, amine hydrogen functionality, and chemical structure similar to TETA so as to minimize difficulties in re-formulation of end use products such as coatings and adhesives.
U.S. Pat. No. 2,705,223 describes epoxy resins cured with polyamides based on polymeric fatty acids and polyethyleneamines.
GB 2,031,431 discloses epoxy resins cured with mixtures of high molecular weight polyoxyalkylene polyamines and N,N′-bis(3-aminopropyl)ethylenediamine.
U.S. Pat. No. 4,463,157 discloses self-curing amide-group-containing aminourea resins produced from a polyaminoamide which has been produced from polyalkylene-polyamines reacted with fatty acids and/or from polyalkylene-polyamines reacted with dimer fatty acids. Table 1 of this patent shows the product of reaction of N,N′-bis(3-aminopropyl)ethylenediamine with ricinene fatty acid.
EP 134,970 describes similar polyaminoamides.